Explanation
Area of front wall = \(9 \times 24 = 216\) sq. ft.
Area of back wall \(9 \times 24 = 216\)sq. ft.
Area of side wall =\( 9 \times 18 = 162\)sq. ft.
Area of other side wall = \(9 \times 18 = 162\) sq. ft.
Total area of walls =\( 216 + 216 + 162 + 162 = 756 \)sqft.
\(756 \div 9 = 84\) sq. yd.